A new synthetic entry to phosphinophosphinidene complexes. Synthesis and structural characterisation of the first side-on bonded and the first terminally bonded phosphinophosphinidene zirconium complexes [mu-(1,2:2-eta-tBu2P=P)[Zr(Cl)Cp2]2] and [[Zr(PPhMe2)Cp2](eta1)-P-PtBu2)

The reactions of lithiated diphosphanes with transition metal chlorides constitute a new general entry to phosphinophosphinidene complexes: the reaction of Cp2ZrCl2(Cp = C5H5) with tBu2P-P(SiMe3)Li (molar ratio approximately 1:1) yields [mu-(1,2:2-eta-tBu2P=P)[Zr(Cl)Cp2]2]; the reaction of Cp2ZrCl2 with tBu2P-P(SiMe3)Li (molar ratio approximately 1:2) and an excess of PPhMe2 in DME yields the first terminally bonded phosphinophosphinidene complex, [[Zr(PPhMe2)Cp2](eta1-P-PtBu2)].     

Cationic Ti(IV) and neutral Ti(III) titanocene-phosphinoaryloxide frustrated Lewis pairs: hydrogen activation and catalytic amine-borane dehydrogenation

Titanium-phosphorus frustrated Lewis pairs (FLPs) based on titanocene-phosphinoaryloxide complexes have been synthesised. The cationic titanium(IV) complex [Cp(2)TiOC(6)H(4)P((t)Bu)(2)][B(C(6)F(5))(4)] 2 reacts with hydrogen to yield the reduced titanium(III) complex [Cp(2)TiOC(6)H(4)PH((t)Bu)(2)][B(C(6)F(5))(4)] 5. The titanium(III)-phosphorus FLP [Cp(2)TiOC(6)H(4)P((t)Bu)(2)] 6 has been synthesised either by chemical reduction of [Cp(2)Ti(Cl)OC(6)H(4)P((t)Bu)(2)] 1 with [CoCp*(2)] or by reaction of [Cp(2)Ti{N(SiMe(3))(2)}] with 2-C(6)H(4)(OH){P((t)Bu)(2)}. Both 2 and 6 catalyse the dehydrogenation of Me(2)HN·BH(3).     

Reactivity of lanthanocene hydroxides toward ketene, isocyanate, lanthanocene alkyl, and triscyclopentadienyllanthanide complexes

The reactivity of [Cp(2)Ln(mu-OH)(THF)]2 (Ln = Y (1), Er (2), Yb (3)) toward PhEtCCO, PhNCO, Cp3Ln, [Cp2Ln(mu-CH3)]2, and the LiCl adduct of Cp2Ln(n)Bu(THF)x was examined. In all cases, OH-centered reactivity is observed: complexes 1-3 react with PhEtCCO to form the O-H addition products [Cp2Ln(mu-eta1:eta2-O2CCHEtPh)]2 (Ln = Yb (5), Er (6), Y (7), respectively, for 1-3), whereas treatment of 1 with PhNCO affords the addition/CpH-elimination/rearrangement product [{Cp2Y(THF)}2(mu-eta2:eta2-O2CNPh)] (8), which contains an unusual PhNCO(2) dianionic ligand. Analogous compound [Cp2Ln(THF)]2(mu-eta2:eta2-O2CNPh) (Ln = Yb (9), Er (10)) and 8 can be obtained in a higher yield by treatment of [Cp2Ln(mu-OH)(THF)]2 with PhNCO followed by reaction with the corresponding Cp3Ln. However, attempts to prepare the corresponding heterobimetallic complex by reacting stoichiometric amounts of [Cp2Y(mu-OH)(THF)]2 with PhNCO followed by treating it with Cp3Yb are unsuccessful. Instead, only rearrangement products 8 and 9 are obtained. Furthermore, the reaction of 3 with [Cp2Yb(mu-CH3)]2 or Cp3Yb forms oxo-bridged compound [Cp2Yb(THF)]2(mu-O) (11), whereas the reaction of [Cp2ErCl]2 with Li(n)Bu followed by treatment with 2 affords unexpected mu-oxo lanthanocene cluster (Cp2Er)3(mu-OH)(mu3-O)(mu-Cl)Li(THF)4 (12). In contrast to 1 and 2, 3 shows a strong tendency to undergo the intermolecular elimination of CpH at room temperature, giving trinuclear species [Cp2Yb(mu-OH)]2[CpYb(THF)](mu3-O) (4). The single-crystal X-ray diffraction structures of 1, 2, and 4-12 are described. All the results offer an interesting contrast to transition- and main-metal hydroxide complexes.     

利用原位氟化保护层改善三维锡锂合金/碳纸负极贫电解液下性能

金属锂具有最高的理论比容量(3860 mAh·g^?1)和最低的还原电势(?3.04 V),是新型高能量密度电池负极材料的最佳选择之一。然而由于金属锂负极表面自发生成的固态电解质界面(SEI)十分不稳定,导致锂枝晶的产生和电池容量快速衰减,严重限制了锂金属电池的商业化应用。因此,本工作利用碳酸双(2,2,2-三氟乙基)酯(DTFEC)添加剂在三维锡锂合金/碳纸负极(SnLi/Cp)表面原位构筑了高机械强度和离子穿透性的含氟化物(LiF和SnF2)保护层,有效地改善了锂负极的倍率性能和循环稳定性。结果显示,SnLi/Cp对称电池在8 mA·cm^?2的电流密度下经过100次循环后过电位仅为90 mV。当将电解液降低到12μL(1.5μL·(mAh)?1)时,在5 mA·cm^?2的电流密度下对称电池仍具有优异的稳定性;SnLi/Cp||NMC811电池在1C(1.5 mA·cm^?2)条件下能稳定循环300圈以上,库伦效率高达98.1%。这种方法能够显著改善锂金属负极的循环稳定性,有助于实现高能量密度锂金属电池的实际应用。     

Synthesis and structural characterization of tris(2-seleno-1-mesitylimidazolyl) hydroborato complexes: a new type of strongly electron donating tripodal selenium ligand

A new tripodal ligand that features three selenium donors, namely the tris(2-seleno-1-mesitylimidazolyl)hydroborato ligand, [Tse(Mes)], has been constructed via the reaction of KBH(4) with 1-mesitylimidazole-2-selone; comparison of the IR spectroscopic data of [Tse(Mes)]Re(CO)(3) with those of a variety of related LRe(CO)(3) complexes demonstrates that the [Tse(Mes)] ligand is more strongly electron donating than Cp, Cp*, [Tp], [Tp(Me(2))] and [Tm(Mes)] ligands.     

Über die natur der übergangsmetall-kohlenstoff-σ-bindung: IX. Über die darstellung und charakterisierung von η5-cyclopentadienyl-triphenylphosphin-nickel-η1-thioanisolyl und seine thermische zersetzung in nickelthiophenolatokomplexe

The reaction of Cp(PPh₃)NiCl (Cp = η⁵-C₅H₅) with PhSCH₂Li gives Cp(PPh₃)Ni(η¹-CH₂SPh) (I), which has been isolated as green crystals and characterized by elemental analysis, magnetic measurement, ¹H NMR and mass spectroscopic investigations and by protolysis to form PhSCH₃. Cp₂Ni also reacts with PhSCH₂Li in the presence of PPh₃ to give I containing 5–10% of Cp(PPh₃)NiSPh (II) and about 1% of [CpNiSPh]₂ (III) as impurities. In the absence of PPh₃, III is formed, with the release of ethylene and cyclopropane, even at a temperature of ?20°C. For comparison, II has been synthesized from Cp₂Ni, PPh₃ and LiSPh and from the reaction of III with PPh₃.I decomposes in boiling benzene to give II (ca. 33%) and III (ca. 13%). The conversion of the thioanisolyl into thiophenolato complexes can be understood on assuming that {CpNi(η²-CH₂SPh)} is formed as an unstable intermediate.     

Synthesis and X-ray crystal structure of a novel organometallic (μ3-oxido)(μ3-imido) trinuclear iridium complex

Reaction of the organometallic aqua ion [Cp*Ir(H(2)O)(3)](2+) with tert-butyl(trimethylsilyl)amine in acetone yielded a novel trinuclear (μ(3)-oxido)(μ(3)-imido)pentamethylcyclopentadienyliridium(III) complex, [(Cp*Ir)(3)(O)(N(t)Bu)](2+). Single crystal structure analyses show the complex can be isolated both in the double salt ((t)BuNH(3))[(Cp*Ir)(3)(O)(N(t)Bu)](CF(3)SO(3))(3) (1) and in the simple triflate [(Cp*Ir)(3)(O)(N(t)Bu)](CF(3)SO(3))(2) (2). The double salt is stabilized by hydrogen bonding between the tert-butylammonium ion and the three triflate anions. It is the first time that a trinuclear (μ(3)-oxido)(μ(3)-imido) transition metal complex has been structurally characterized.     

Pentamethylcyclopentadienyl-übergangsmetall-komplexe: X. Halbsandwichkomplexe des Fe und Ni als reaktive zwischenprodukte

Reaction of NiX₂·DME (X = Cl, Br; DME = 1,2-Dimethoxyethane) with Cp′Li (Cp′ = η⁵-C₅Me₅) in THF at ?10°C yields as intermediates dimeric halogeno complexes [Cp′NiX]₂ (I) as shown by mass spectroscopy. 1 reacts with neutral and anionic donor ligands viz. PPh₃ to Cp′Ni(PPh₃)X, 1,5-COD to [Cp′NiCOD]⁺, CpNa to CpCp′Ni and with COTLi₂ to (Cp′Ni)₂COT (COT = cyclooctatetraene). Analogously the reaction product from FeBr₂·DME and Cp′Li at ?80°C in THF is converted by CpNa to CpCp′Fe and by CO to Cp′Fe(CO)₂Br.     

Syntheses and structures of the first terminal phosphanylphosphido complex of hafnium [Cp2Hf(Cl){η(1)-(Me3Si)P-P(NEt2)2}] and the first zirconocene-phosphanylphosphinidene dimer [Cp2Zr{μ(2)-P-P(NEt2)2}2ZrCp2

Reactions of (Et(2)N)(2)P-P(SiMe(3))Li with [Cp(2)MCl(2)] (M = Zr, Hf) in toluene or pentane yield the related terminal phosphanylphosphido complexes [Cp(2)M(Cl){η(1)-(Me(3)Si)P-P(NEt(2))(2)}]. The solid state structure of [Cp(2)Hf(Cl){η(1)-(Me(3)Si)P-P(NEt(2))(2)}] was established by single crystal X-ray diffraction. The reaction of (Et(2)N)(2)P-P(SiMe(3))Li with [Cp(2)ZrCl(2)] in THF or DME solutions leads to the formation of deep red crystals of the first neutral diamagnetic zirconocene-phosphanylphosphinidene dimer [Cp(2)Zr{μ(2)-P-P(NEt(2))(2)}(2)ZrCp(2)]. The molecular structure of this compound was confirmed by X-ray diffraction. The reactions of (R(2)N)(2)P-P(SiMe(3))Li with [CpZrCl(3)] yield the related tetraphosphetanes R(2)NP(μ(2)-PSiMe(3))(2)PNR(2), which apparently are formed as a result of a transfer of NR(2) groups from a P atom to the Zr atom.     

A new route into single-crystalline partially oxidized cobalt compounds: reactions with zintl-type hexaselenodistannate(III) K6Sn2Se6 as mild oxidant

Reactions of K6Sn2Se6 (1) with [Cp*CoCl]2 were investigated in order to probe the stability of the formal +3 oxidation state at Sn and possible ligand properties of heteroatomic zintl-type anion "Sn2Se6(6)- ". From these experiments, we obtained the following compounds that are oxidized to different extent as a result of the reaction with SnIII: [Cp2*Co][Cl2Co(mu2-Cl)2Li(thf)2] (2), [(Cp*Co)3(mu-Se)2] (3), [(Cp*Co)3(mu3-Se)2][Cl2Co(mu2-Cl)2Li(thf)2] (4), and [(Cp*Co)4(mu3-Se)4] (5). These compounds were structurally characterized by single-crystal X-ray diffractometry. It shows that the reaction conditions strongly affect the type and oxidation state of the isolated product. Two of the observed compounds, 3 and 4, are closely related both structurally and electronically; this is discussed and further illustrated by cyclovoltammetric measurements. The choice of the terminal Cp* ligand attached to the transition metal in the reactand complex is assumed to be basically dependent for the alignment of unexpected structural details when compared with known compounds of similar compositions. In conclusion, 1 is observed to act as mild oxidant as well as selenide donor, but is not in the position to keep its Sn-Se framework under the given reaction conditions.     

An Experimental and Computational Investigation Rules Out Direct Nucleophilic Addition on the N2 Ligand in Manganese Dinitrogen Complex [Cp(CO)2Mn(N2)]

We have re-examined the reactivity of the manganese dinitrogen complex [Cp(CO)₂Mn(N₂)] ( 1 , Cp=η⁵-cyclopentadienyl, C₅H₅) with phenylithium (PhLi). By combining experiment and density functional theory (DFT), we have found that, unlike previously reported, the direct nucleophilic attack of the carbanion onto coordinated dinitrogen does not occur. Instead, PhLi reacts with one of the CO ligands to provide an anionic acylcarbonyl dinitrogen metallate [Cp(CO)(N₂)MnCOPh]Li ( 3 ) that is stable only below −40 °C. Full characterization of 3 (including single crystal X-ray diffraction) was performed. This complex decomposes quickly above −20 °C with N₂ loss to give a phenylate complex [Cp(CO)₂MnPh]Li ( 2 ). The latter compound was erroneously formulated as an anionic diazenido compound [Cp(CO)₂MnN(Ph)=N]Li in earlier reports, ruling out the claimed and so-far unique behavior of the N₂ ligand in 1 . DFT calculations were run to explore both the hypothesized and the experimentally verified reactivity of 1 with PhLi and are fully consistent with our results. Direct attack of a nucleophile on metal-coordinated N₂ remains to be demonstrated.     

Highly selective epoxidation of styrene using a transition metal-aluminium(III) complex containing the [MeAl(2-py)3]- anion (2-py = 2-pyridyl)

The reactions of [MeAl(2-py)3Li.thf] (1) with FeCl2 or Cp2Mn in toluene-thf give simple access to the Group 13-transition metal heterometallic complexes [{MeAl(2-py)3}2M][M = Fe (2), Mn (3)]; complex has been shown to be a highly selective styrene epoxidation catalyst in air.     

The P(bth)2- anion as a Janus head staple between lithium and manganese (bth = benzothiazol-2-yl, C7H4NS)

Deprotonation of HP(bth)2 (1) affords the lithium phosphanide [(Et2O)2Li(bth)2P], (2) with both nitrogen atoms coordinated to the lithium atom while in the heterobimetallic complex [Li(bth)2P{Mn(CO)2Cp}2](n) (3) additionally the phosphorus atom micro-bridges two Mn(CO)2Cp residues.     

Highly Strained Heterometallacycles of Group 4 Metallocenes with Bis(diphenylphosphino)amide Ligands

A study regarding coordination chemistry of the bis(diphenylphosphino)amide ligand Ph(2) P-N-PPh(2) at Group?4 metallocenes is presented herein. Coordination of N,N-bis(diphenylphosphino)amine (1) to [(Cp(2) TiCl)(2) ] (Cp=η(5) -cyclopentadienyl) generated [Cp(2) Ti(Cl)P(Ph(2) )N(H)PPh(2) ] (2). The heterometallacyclic complex [Cp(2) Ti(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3?Ti) can be prepared by reaction of 2 with n-butyllithium as well as from the reaction of the known titanocene-alkyne complex [Cp(2) Ti(η(2) -Me(3) SiC(2) SiMe(3) )] with the amine 1. Reactions of the lithium amide [(thf)(3) Li{N(PPh(2) )(2) }] with [Cp(2) MCl(2) ] (M=Zr, Hf) yielded the corresponding zirconocene and hafnocene complexes [Cp(2) M(Cl){κ(2) -N,P-N(PPh(2) )(2) }] (4?Zr and 4?Hf). Reduction of 4?Zr with magnesium gave the highly strained heterometallacycle [Cp(2) Zr(κ(2) -P,P-Ph(2) P-N-PPh(2) )] (3?Zr). Complexes 2, 3?Ti, 4?Hf, and 3?Zr were characterized by X-ray crystallography. The structures and bondings of all complexes were investigated by DFT calculations.     

Synthesis, reactivity, spectroscopic characterization, X-ray structures, PGSE, and NOE NMR studies of (eta5-C5Me5)-rhodium and -iridium derivatives containing bis(pyrazolyl)alkane ligands

Rhodium(III) and iridium(III) complexes containing bis(pyrazolyl)methane ligands (pz = pyrazole, L' in general; specifically, L1 = H2C(pz)2, L2 = H2C(pzMe2)2, L3 = H2C(pz4Me)2, L4 = Me2C(pz)2), have been prepared in a study exploring the reactivity of these ligands toward [Cp*MCl(mu-Cl)]2 dimers (M = Rh, Ir; Cp* = pentamethylcyclopentadienyl). When the reaction was carried out in acetone solution, complexes of the type [Cp*M(L')Cl]Cl were obtained. However, when L1 and L2 ligands have been employed with excess [Cp*MCl(mu-Cl)]2, the formation of [Cp*M(L')Cl][Cp*MCl3] species has been observed. PGSE NMR measurements have been carried out for these complexes, in which the counterion is a cyclopentadienyl metal complex, in CD2Cl2 as a function of the concentration. The hydrodynamic radius (rH) and, consequently, the hydrodynamic volume (VH) of all the species have been determined from the measured translational self-diffusion coefficients (Dt), indicating the predominance of ion pairs in solution. NOE measurements and X-ray single-crystal studies suggest that the [Cp*MCl3]- approaches the cation, orienting the three Cl-legs of the "piano-stool" toward the CH2 moieties of the bis(pyrazolyl)methane ligands. The reaction of 1 equiv of [Cp*M(L')Cl]Cl or [Cp*M(L')Cl][Cp*MCl3] with 1 equiv of AgX (X = ClO4 or CF3SO3) in CH2Cl2 allows the generation of [Cp*M(L')Cl]X, whereas the reaction of 1 equiv of [Cp*M(L')Cl] with 2 equiv of AgX yields the dicationic complexes [Cp*M(L')(H2O)][X]2, where single water molecules are directly bonded to the metal atoms. The solid-state structures of a number of complexes were confirmed by X-ray crystallographic studies. The reaction of [Cp*Ir(L')(H2O)][X]2 with ammonium formate in water or acetone solution allows the generation of the hydride species [Cp*Ir(L')H][X].     

Preparation and physical properties of early-late heterobimetallic compounds featuring Ir-M bonds (M = Ti, Zr, Hf)

Treatment of Cp*Ir N(t)Bu (1) with the appropriate metallocene equivalent is an effective route for the preparation of the heterobimetallic complexes Cp*Ir(μ-N(t)Bu)MCp(2) (2-M, M = Ti, Zr, Hf). The electronic structures of the isostructural series of compounds, 2-M, are described with reference to single-crystal X-ray, Raman, UV-vis, and cyclic voltammetry data. Density functional theory (DFT) calculations were used to aid in the interpretation of this experimental work. Treatment of the zirconium or hafnium congeners with 2,6-lutidinium triflate leads to protonation of the Ir-M bond, to afford Cp*Ir(μ-N(t)Bu)(μ-H)MCp(2)OTf (3-M, M = Zr, Hf). Compound 3-Zr was characterized by single-crystal X-ray diffraction and independently prepared by the reaction of 1 and Cp(2)Zr(H)Cl in the presence of Me(3)SiOTf. In reactions analogous to those for 2-Zr, 2-Hf reacts with S(8) and aryl azides to insert an S-atom or aryl azide fragment into the metal-metal bond, yielding Cp*Ir(μ-N(t)Bu)(μ-S)HfCp(2) (6-Hf) and Cp*Ir(μ-N(t)Bu)(N(3)Ph)HfCp(2) (4-Hf), respectively. Heating 4-Hf results in N(2) extrusion to form Cp*Ir(μ-N(t)Bu)(NPh)HfCp(2) (5-Hf). The kinetics of the latter reaction were studied to obtain activation parameters and a Hammett trend; these data are compared to those for the analogous reaction involving Ir-Zr heterobimetallics.     

Stepwise nucleophilic substitution of manganocene, syntheses and structures of the dimer [CpMn(hpp)]2 and the unusual manganate cage [LiMn(hpp)3]2 (hppH = 1,3,4,6,7,8-hexahydro-2H-pyrimido[1,2,a]pyrimidine)

While the nucleophilic substitution reaction of manganocene [Cp(2)Mn] with Li(hpp) (1 : 1 equivalents) gives the neutral dimer [CpMn(hpp)]2 (1), further substitution of the Cp ligands leads to the unusual dimeric manganate cage compound [LiMn(hpp)3]2 (2), generated by the dimerisation of a simple tris-organomanganate monomer.     

Superbulky metallocene complexes of the heavier alkaline-earth metals strontium and barium

Superbulky sandwich complexes with the cyclopentadienyl ligand (4-nBu-C(6)H(4))(5)Cp (abbreviated here as Cp(BIG)) have been prepared by reaction of Cp(BIG)H with benzylic strontium or barium reagents. Both metallocenes have been structurally characterized by single crystal X-ray diffraction. Even for the larger metallocene (Cp(BIG))(2)Ba a highly symmetric sandwich complex with parallel Cp rings was isolated (Cp(center)-Ba = 2.667(1) A). Both structures show evidence for a C-HC(pi) network between the Cp ligands. These attractive forces induce an inward out-of-plane bending of the aryl substituents (Sr 3.4(2) degrees ; Ba 5.3(2) degrees ). A linear correlation between this bending angle and metal size has been found.     

Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)]. Reaction of the n=2 reagent with [Cp(2)ZrCl(2)] leads to disubstitution, but [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)] is in equilibrium with the product of β-hydride elimination [Cp(2)Zr(H){NH(2)B(C(6)F(5))(2)H}], which proves to be the major isolated solid. The analogous reaction with [Cp(2)HfCl(2)] gives a mixture of [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)] and the N-H activation product [Cp(2)Hf{NHB(C(6)F(5 )(2)H}]. [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)]·PhMe and [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]·4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]?PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp(2)Hf{NHB(C(6)F(5))(2)H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp(2)MMe(μ-Me)B(C(6)F(5))(3)] (M=Zr, Hf) with Li[NH(2)B(C(6)F(5))(n)H(3-n)] (n=2) results in [Cp(2) MMe{NH(2)B(C(6)F(5))(2)H}] complexes, for which the spectroscopic data, particularly (1)J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp'(2)ZrMe(μ-Me)B(C(6)F(5))(3)] precursor (Cp'=1,3-C(5)H(3)(SiMe(3))(2) , n=1 or 2) to give [Cp'(2)ZrMe{NH(2)B(C(6)F(5))(n)H(3-n)}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp'(2)HfMe(2)] and the formation of Li[HB(C(6)F(5))(3)] through hydride abstraction.     

Yttrium Complexes of Arsine,Arsenide, and Arsinidene Ligands

Deprotonation of the yttrium–arsine complex [Cp′₃Y{As(H)₂Mes}] ( 1 ) (Cp′=η⁵‐C₅H₄Me, Mes=mesityl) by nBuLi produces the μ‐arsenide complex [{Cp′₂Y[μ‐As(H)Mes]}₃] ( 2 ). Deprotonation of the As H bonds in 2 by nBuLi produces [Li(thf)₄]₂[{Cp′₂Y(μ₃‐AsMes)}₃Li], [Li(thf)₄]₂[ 3 ], in which the dianion 3 contains the first example of an arsinidene ligand in rare‐earth metal chemistry. The molecular structures of the arsine, arsenide, and arsinidene complexes are described, and the yttrium–arsenic bonding is analyzed by density functional theory.